The neighbor contacted police, and Sheehan was pronounced dead at the scene by paramedics, police said.

According to Trooper Chris Kay, an autopsy performed Thursday determined the cause of death was a heart attack.

Police said an initial investigation indicated that Sheehan may have been driving the bulldozer when he struck the propane tank.

Authorities do not believe the heart attack was caused by inhalation of the propane — which police said was unlikely outdoors where the fumes were not concentrated.Sheehan appeared to have a heart attack prior to striking the tank, police said.